Parasitic suppressor for cavity resonator devices



July 25, 1950 s. vca. M NEES 2,516,522

PARASITIC SUPPRESSOR FOR CAVITY RESONATOR DEVIbES Filed March 1, 1946 FIG.|

INVENTOR. STERLING G. M0 NEES 1 ar 1 40mm Q/M A TTOR/VE Y Patented July 25, 1950 l ;z U NlTED STATES PATENT OFFICE PARASITIC SUPPRESSOR FOR CAVITY RESONATOR DEVICES Sterling G. McNees, Woods Hole, Mass, assignor to the United States of America as represented by the Secretary of War Application Marchl, 1946, Serial No. 651,315

4 Claims. 1

This invention relates to electronic devices, and, more particularly, to a vacuum tube of the resnatron type for generating ultra-high frequency power.

In the Operation of a resnatron, an undesired or, parasitic oscillation of a mode other than that desired may be developed. It is an object of this invention to suppress or minimize the effect of such a parasitic oscillation.

, A feature of the invention comprises coupling a, suitably proportioned tuned circuit with one of the cavities of a resnatron, for suppressing or minimizing an undesired mode of oscillation by the tube.

In accordance with the invention, a tuned or tunable series resonant circuit comprising a variable capacitance and an inductance, together with an inductive loop for coupling the resonant circuit into one of the resonant cavities of a resnatron, is associated with a vacuum tube of the resnatron type. The capacitance may be provided by a pair of metallic plates, one of which is stationary and connected with the inductive loop, and the other of which is attached to one end of the coil providing the inductance. The inductance may comprise a single turn of metallic rod, for example, of iron, connected with one of the capacitance plates and at its other end connected with a suitable screw-thread adjustment for longitudinal adjustment of one capacitance plate relative to the other capacitance plate. The resonant circuit is tunedto the mode that it is desired to suppress, and sufficient dissipation is provided in order to suppress or control the undesired oscillation.

A more complete understanding of the invention may be derived from the specific description that follows, taken in conjunction with the appended drawing, wherein:

Fig. 1 is a schematic representation of a resnatron type tube in which the invention may be incorporated; and

Fig. 2 is a cross-sectional view of a parasitic oscillation suppressor in accordance with the invention.

With reference to the drawing, Fig. l is a line representation of a vacuum tube l of the resnatron type adapted for oscillation in the threequarter wavelength mode. The device comprises a cathode unit I2, a control grid structure M, a screen or accelerating grid structure [6, and an anode structure 18. There are two resonant circuits 20, 22. The cavity resonator 20, called the cathode cavity, is formed between the cathode and the control grid structure, and is electrically equivalent, at the resonant frequency, to a three-quarter wavelength transmission line short-circuited at the lower end and open-cir-,

' resonant cavities are interconnected or coupled by one or more feedback wires or probes 24, that may be mounted on the cathode structure and that extend through the grids provided by the control and screen grid structures toward and in spaced relation to the anode. The tube may include a one-quarter wavelength control gridcathode radio frequency by-pass condenser 26,: and a second one-quarter wavelength screen;

grid-anode radio frequency by-pass condenser 28. The cathode structure may include a flexible bellows or Sylphon 29, capped by a capacitance plate 30 adjustable relative to the control grid under control of a tuning rod 32, to permit; adjustment in the tuning of the cathode cavity,

The anode cavity tuning may be adjusted under control of a tuning rod 34 for adjusting the posi tion of a portion of the anode structure wall relative to the screen grid structure.

transferred to a suitable utilization circuit (not shown) through a coupling loop 36.

It has been observed that, in a resnatron of the type described, an undesired orparasitic mode of oscillation, a so-called one-quarter wavelength mode, may be present to an undesirable degree. This mode apparently is especially likely to occur when the desired three-quarter wavelength mode is being heavily loaded for low Q operation. In this case the one-quarter wavelength mode, which is normally not heavily loaded, probably has a higher Q than the desired mode. The tendency of the oscillating system would be to oscillate in a high Q rather than in a low Q mode. It has been found, in accordance with this invention, that such a parasitic oscillation may be suppressed by means of a series resonant circuit coupled to the anode cavity, heavily loaded, and tuned to the undesired mode.

The power developed by the resnatron in operation may be,

Fig. 2 illustrates a device for providing such a resonant circuit to be coupled to the anode cavity through a coupling loop 40.

The resonant circuit comprises a variable or adjustable capacitor 42 and an inductance coil or loop 44. The capacitor comprises a pair of metallic circular disks orplates 46, 48, for example, of brass, the disk 48 being secured to one end 50 of the loop 40 which may be formed of a short length of copper rod. The movable plate 48 is secured to one end 52 of the inductance coil 44 which may be formed of a short length of metallic rod, preferably of a higher resistivity material, for example, iron, the other end 54 of coil being secured to a circular plate assembly 56, adjustable in position between stationary circular plate assemblies 58, 60 under control of screw-thread adjustment 62, manually operated by a suitable handwheel 54. The assemblies 58, 6B are separated by four equally spaced spacers 66 (two shown), that serve, additionally, as guides for the plate assembly 56. A flexible bellows or Sylphon 68, of'thin sheet material, may be disposed between the movable assembly 55 and the stationary assembly 58. The loop 40 may besecured to a collar member '59, in turn fastened to a ring or cap member 12 closing one end of a tubular enclosure 14 forthe capacitor 42 and coil M, the tubular enclosure being secured to the plate assembl 58. Members 40, 44 are shown in broken section to indicate their rod-like character. Members 40, l0, l2, l4 and 63 and assemblies 56, 53 may be secured together, where adjacent, by solder. In a device constructed in accordance with the invention, disks 46, it were of the order of one and one-half inches in diameter, and the coil 44 was of a rod of the order of three-sixteenths inch in diameter.

The incorporation in a resnatron of the described-suppressor unit or device, tuned to the undesired oscillation or mode, enables loadin the undesired mode with the required dissipation, introducing sufiicient loss into the undesired mode to prevent or suppress oscillation thereat.

Obviously;'changes in materials, proportions and configuration of the suppressor unit may be made without departing from the spirit of the invention, and obvious application of the inventive concept to other types of cavity resonators Will'readily occur to those skilled in the art. Although the invention has been described with ref erence to a single embodiment, it is not restricted thereto and the invention shall be considered as limited only by the requirements of the prior art and the appended claims.

What is claimed is:

1. In combination, a vacuum tube of the resnatron type for generating ultra-high frequency power in a preassigned mode but also generating an undesired oscillation, and means to suppress said undesired oscillation located externally of said resnatron but coupled into one of the resonant cavities of said resnatron, said means comprising a variable capacitance and an inductance connected in series and tuned to the frequency of the undesired oscillations, the said inductance being formed from a metallic rod of a higher resistivity than the remainder of said circuit.

2. In combination, a cavity resonator for resonance in a preassigned mode but developing an undesired oscillation, and means for suppressing said undesired oscillation located externally of and electrically coupled to said cavity resonator, said means comprising a series connected variable capacitance and inductance tuned to the frequency of the undesired oscillation, said inductance being formed of a metallic rod of higher resistivity material than the remainder of said circuit.

3. The combination recited in claim 2 in which said capacitance is provided by a pair of spaced metallic discs, one of said discs being supported at one end of said metallic rod.

4. A high frequency structure com-prising a, first stationary plate assembly and a second stationary plate assembl having an opening at its center. spacer rods attached to said stationary plate assemblies holding them in parallel spaced relationship, a movable plate assembly movably attached at its outer edges to said spacer rods between said stationary plate assemblies, means to move said movable plate assembly along said spacer rods, a metallic rod bent in the form of an inductance coil having one extended end passing axially thru said opening, said end bein attached to said movable plate assembly and supported thereby, the other end of said metallic rod being attached to and supporting a movable metal plate, a fixed metal plate spaced from said movable metal plate to form a condenser therewith, a pick-up. loop with one end connected to and supporting said fixed metal plate, the other end of said pick-up. loop being attached to means surrounding'said inductance coil and said condenser, the said means being connected with said second stationary plate assembly outside of its center opening, and a Sylphon bellows surrounding the extended end of said metallic rod, said bellows being attached to said second stationary plate assembly and said movable plate assembly.

STERLING G. McNEES.

REFERENCES CITED Thefollowing references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 2,030,178 Potter Feb. 11, 1936' 2,270,416 Cork Jan. 20, 1942 2,417,789 Spencer Mar. 18, 194? 2,419,172 Smith Apr. 15, 1947 2,439,388 Hansen Apr. 13, 1948 

